George, 68, likes to work a room. He teases and needles aides, lawmakers or reporters until he gets a rise. He talks about issues in broad strokes, believes in delegating and sometimes mangles his English.

Several inches taller, Jeb, 61, reads footnotes, emails frenetically and talks in full, wonky paragraphs. But in political settings, he sometimes seems to eye the exit, calculating how to get from here to there with the least fuss. “Former President Bush is much more instantly gregarious, a bigger personality,” said Ari Fleischer, George W. Bush’s first White House press secretary. “When he walks into a room, he just takes it over, by style and by charm. Jeb is more intellectual, more pensive and more articulate.”

Jeb Bush has a quick wit, Mr. Fleischer added, but it is softer than his brother’s.

“Jeb is very much a policy wonk and comes across that way,” he said. “Former President Bush was much more big picture, strong leader, defined things in immediately clear moral terms.”

They come at politics from different angles. “Public service seems to be a calling for George Senior and George Junior, whereas for Jeb it is about a mission,” said Clint Bolick, who wrote a book on immigration with Jeb Bush. “It’s about policy and ideas. I never really got the impression that either his dad or his brother were really motivated by ideas and policies. For Jeb, politics is a means to an end rather than an end in itself.”